Method for ablating with needle electrode

ABSTRACT

A method for ablating tissue in or around the heart to create an enhanced lesion is provided. The distal end of a catheter including a needle electrode at its distal end is introduced into the heart. The distal end of the needle electrode is introduced into the tissue. An electrically-conductive fluid is infused through the needle electrode and into the tissue. The tissue is ablated after and/or during introduction of the fluid into the tissue. The fluid conducts ablation energy within the tissue to create a larger lesion than would be created without the introduction of the fluid.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of U.S. patent application Ser. No.10/694,118, filed Oct. 27, 2003, now U.S. Pat. No. 7,207,989, andentitled METHOD FOR ABLATING WITH NEEDLE ELECTRODE, the entire contentof which is incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to methods for enhancing ablation by infusing aconductive fluid through a needle electrode.

BACKGROUND OF THE INVENTION

Radiofrequency (RF) ablation of cardiac and other tissue is a well knownmethod for creating thermal injury lesions at the tip of an electrode.Radiofrequency current is delivered between a skin (ground) patch andthe electrode. Electrical resistance at the electrode-tissue interfaceresults in direct resistive heating of a small area, the size of whichdepends upon the size of the electrode, electrode tissue contact, andcurrent (density). See Avitall B, Helms R. Determinants orRadiofrequency-Induced Lesion Size in Huang S K S, Wilber D J (eds.):Radiofrequency Catheter Ablation of Cardiac Arrhythmias: Basic Conceptsand Clinical Applications, 2nd ed. Armonk, N.Y., Futura PublishingCompany, Inc., 2000: 47-80. Further tissue heating results fromconduction of heat within the tissue to a larger zone. Tissue heatedbeyond a threshold of approximately 50-55° C. is irreversibly injured(ablated). See Nath S, and Haines D E. Pathophysiology of LesionFormation by Radiofrequency Catheter Ablation, in Huang S K S, Wilber DJ (eds.): Radiofrequency Catheter Ablation of Cardiac Arrhythmias: BasicConcepts and Clinical Applications, 2nd ed. Armonk, N.Y., FuturaPublishing Company, Inc., 2000: 26-28.

Resistive heating is caused by energy absorption due to electricalresistance. Energy absorption is related to the square of currentdensity and inversely with tissue conductivity. Current density varieswith conductivity and voltage and inversely with the square of radiusfrom the ablating electrode. Therefore, energy absorption varies withconductivity, the square of applied voltage, and inversely with thefourth power of radius from the electrode. Resistive heating, therefore,is most heavily influenced by radius, and penetrates a very smalldistance from the ablating electrode. The rest of the lesion is createdby thermal conduction from the area of resistive heating. See Lin J,Physical Aspects of Radiofrequency Ablation, in Huang S K S, Wilber D J(eds.): Radiofrequency Catheter Ablation of Cardiac Arrhythmias: BasicConcepts and Clinical Applications, 2nd ed. Armonk, N.Y., FuturaPublishing Company, Inc., 2000: 14-17. This imposes a limit on the sizeof ablation lesions that can be delivered from a surface electrode.

Theoretical methods to increase lesion size would include increasingelectrode diameter, increasing the area of electrode contact withtissue, increasing tissue conductivity and penetrating the tissue toachieve greater depth and increase the area of contact, and deliveringRF until maximal lesion size has been achieved (60-120 seconds for fullmaturation).

The electrode can be introduced to the tissue of interest directly (forsuperficial/skin structures), surgically, endoscopically,laparoscopically or using percutaneous transvascular (catheter-based)access. Catheter ablation is a well-described and commonly performedmethod by which many cardiac arrhythmias are treated. See Miller J M,Zipes D P. Management of the Patient with Cardiac Arrhythmias. InBraunwald E, Zipes D, Libby P (eds): Heart Disease: A Textbook ofCardiovascular Medicine, 6th Ed. Philadelphia, Pa., W.B. SaundersCompany, 2001: p 742-752. Needle electrodes have been described forpercutaneous or endoscopic ablation of solid-organ tumours, lungtumours, and abnormal neurologic structures. See, for example, McGahan JP, Schneider P, Brock J M, Tesluk H. Treatment of Liver Tumors byPercutaneous Radiofrequency Electrocautery. Seminars in InterventionalRadiology 1993; 10: 143-149; Rossi S, Formari F, Buscarini L.Percutaneous Ultrasound-Guided Radiofrequency Electrocautery for theTreatment of Small Hepatocellular Carcinoma. J Intervent Radiol 1993; 8:97-103; and Livraghi T, Goldberg S N, Lazzaroni S, Meloni F, Monti F,Solbiati L. Saline-enhanced RF tissue ablation in the treatment of liverMetastases. Radiology 1995; 197(P): 140 (abstr)].

Catheter ablation is sometimes limited by insufficient lesion size. Seede Bakker J M T, van Capelle F J L, Janse M J et al. Macroreentry in theinfarcted human heart: mechanism of ventricular tacycardias with a“focal” activation pattern. J Am Coll Cardiol 1991; 18:1005-1014;Kaltenbrunner W, Cardinal R, Dubuc M et al. Epicardial and endocardialmapping of ventricular tachycardia in patients with myocardialinfarction. Is the origin of the tachycardia always subendocardiallylocalized? Circulation 1991; 84: 1058-1071. Stevenson W G, Friedman P L,Sager P T et al. Exploring postinfarction reentrant ventriculartachycardia with entrainment mapping. J Am coll Cardiol 1997; 29:1180-1189. Ablation of tissue from an endovascular approach results notonly in heating of tissue, but of heating of the electrode. When theelectrode reaches critical temperatures, denaturation of blood proteinscauses formation of a high resistance coagulum that limits currentdelivery. Within tissue, overheating can cause evaporation of tissue orblood water and steam bubble formation that can “explode” through themyocardial wall (steam “pops”) with risk of uncontrolled tissuedestruction or undesirable perforation of bodily structures. In cardiacablation, clinical success is sometimes hampered by inadequate lesiondepth and transverse diameter even when using catheters with activecooling of the tip. See Soejima K, Delacretaz E, Suzuki M et al.Saline-cooled versus standard radiofrequency catheter ablation forinfarct-related ventricular tachycardias. Circulation 2001;103:1858-1862. Theoretical solutions have included increasing theelectrode size (increasing contact surface and increasing convectivecooling by blood flow), improving electrode-tissue contact, activelycooling the electrode with fluid infusion, changing the materialcomposition of the electrode to improve current delivery to tissue, andpulsing current delivery to allow intermittent cooling. Needleelectrodes improve contact with tissue and allow deep penetration ofcurrent delivery to areas of interest. Ablation may still be hampered bythe small surface area of the needle electrode such that heating occursat low power, and small lesions are created. Accordingly, a need existsfor a method for creating improved lesions.

SUMMARY OF THE INVENTION

The invention concerns a novel method for endovascular percutaneousablation of mammalian tissue, including cardiac tissue. This inventionis useful for destroying abnormal cardiac tissue such as myocardialreentry circuits causing arrhythmias, hypertrophic cardiomyopathycausing flow obstruction, or other tissues which may be approachedendovascularly. A theoretic increase in the effective size of theelectrode can be achieved by delivering conductive fluid through theneedle. The fluid infiltrates the interstitium of the tissue ofinterest, and conducts current rapidly over a greater volume of tissue,creating a larger area of resistive heating, with a significantly largersurface area, and a consequently significantly larger volume of tissueheated by conductive heating.

In one embodiment, the invention is directed to a method for ablatingtissue in or around the heart to create an enhanced lesion. The distalend of a catheter including a needle electrode at its distal end isintroduced into the heart. The distal end of the needle electrode isintroduced into the tissue. An electrically-conductive fluid is infusedthrough the needle electrode and into the tissue. The tissue is ablatedafter and/or during introduction of the fluid into the tissue. The fluidconducts ablation energy within the tissue to create a larger lesionthan would be created without the introduction of the fluid.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention will bebetter understood by reference to the following detailed descriptionwhen considered in conjunction with the accompanying drawings wherein:

FIG. 1 is a side plan view of a catheter according to the presentinvention;

FIG. 2 is a side cross-sectional view of the proximal shaft, includingthe junction between the proximal shaft and the distal shaft;

FIG. 3 is a side cross-sectional view of the distal shaft showing thearrangement of the electromagnetic mapping sensor, needle electrode andtip electrode;

FIG. 4 is an end cross-sectional view of the distal shaft shown in FIG.3 along line 4-4;

FIG. 5 is an end cross-sectional view of the tip electrode shown in FIG.3 along line 5-5;

FIG. 6 is an enlarged view of the needle electrode assembly shown inFIG. 3;

FIG. 7 is an enlarged side cross-sectional view of the thermocouplemounted in the needle electrode assembly shown in FIG. 3;

FIG. 8 is a side cross-sectional view of the needle control handle wherethe needle is in a retracted position;

FIG. 9 is a graph showing the presence of pops versus power delivered totissue in vitro using a catheter having a needle electrode as describedin Example 1;

FIG. 10 is a graph showing maximum lesion width by power and durationfor lesions created in vitro using a catheter having a needle electrodeas described in Example 1;

FIG. 11 is a graph showing lesion cross-sectional area by depth forlesions created in vivo using a catheter having a needle electrode asdescribed in Example 2;

FIG. 12 is a graph showing impedance during infusion of ionic solutionthrough the needle electrode in vitro as described in Example 3;

FIG. 13 is a graph showing lesion diameter over time of ablation forlesions created using a needle electrode with saline infusion in vitroas described in Example 3; and

FIG. 14 is a graph showing lesion cross-sectional area versus depth forlesions created using a needle electrode with saline infusion in vivo asdescribed in Example 4.

DETAILED DESCRIPTION OF THE INVENTION

In one embodiment of the invention, there is provided a catheterparticularly useful for ablating tissue in the heart. As shown in FIG.1, the catheter comprises an elongated proximal shaft 10 having aproximal shaft 12 and a distal shaft 14. A deflection control handle 16is mounted at the proximal end of the proximal shaft 12, and a needlecontrol handle 17 is attached indirectly to the proximal shaft proximalto the deflection control handle.

With reference to FIG. 2, the proximal shaft 12 comprises a single,central or axial lumen 18. The proximal shaft 12 is flexible, i.e.,bendable, but substantially non-compressible along its length. Theproximal shaft 12 may be of any suitable construction and made of anysuitable material. A presently preferred construction comprises an outerwall 20 made of a polyurethane or nylon. The outer wall 20 comprises animbedded braided mesh (not shown) of stainless steel or the like toincrease torsional stiffness of the proximal shaft 12 so that, when thedeflection control handle 16 is rotated, the distal shaft 14 will rotatein a corresponding manner. The outer diameter of the proximal shaft 12is not critical, but is preferably no more than about 8 French. Likewisethe thickness of the outer wall 20 is not critical.

As shown in FIGS. 2 to 4, the distal shaft 14 comprises a short sectionof tubing 19 having four lumens, namely, a puller wire lumen 22, aninfusion lumen 24, a lead wire lumen 26 and a sensor cable lumen 28. Thetubing 19 is made of a suitable non-toxic material which is preferablymore flexible than the proximal shaft 12. A presently preferred materialfor the tubing 19 is braided polyurethane, i.e., polyurethane with anembedded mesh of braided stainless steel or the like. The outer diameterof the distal shaft 14, like that of the proximal shaft 12, ispreferably no greater than about 8 French. The size of the lumens is notcritical. In a particularly preferred embodiment, the distal shaft 14has an outer diameter of about 0.096 inch, the infusion lumen 24 has adiameter of about 0.044 inch, and the puller wire lumen 22, lead wirelumen 26 and sensor cable lumen 28 each have a diameter of about 0.022inch.

A preferred means for attaching the proximal shaft 12 to the distalshaft 14 is illustrated in FIG. 2. The proximal end of the distal shaft14 comprises an outer circumferential notch 30 that receives the innersurface of the outer wall 20 of the proximal shaft 12. The distal shaft14 and proximal shaft 12 are attached by glue or the like.

With reference to FIGS. 3 and 5, mounted at the distal end of the distalshaft 14 is a tip electrode 32. For clarity, FIG. 3 only shows two ofthe four lumens of the distal shaft 14. Preferably the tip electrode 32has a diameter about the same as the outer diameter of the tubing 19.The tip electrode 32 is connected to the tubing 19 by a plastic housing34, preferably made of polyetheretherketone (PEEK). The proximal end ofthe tip electrode 32 is notched circumferentially and fits inside thedistal end of the plastic housing 34 and is bonded to the housing bypolyurethane glue or the like. The proximal end of the plastic housing34 is bonded with polyurethane glue or the like to the distal end of thetubing 19 of the distal shaft 14. Alternatively, the tip electrode 32can be mounted directly to the distal end of the flexible tubing 19 ofthe distal shaft 14.

Mounted on the distal end of the plastic housing 34 is a ring electrode38. The ring electrode 38 is slid over the plastic housing 34 and fixedin place by glue or the like. If desired, additional ring electrodes maybe used and can be positioned over the plastic housing 34 and/or overthe flexible tubing 19 of the distal shaft 14.

The tip electrode 32 and ring electrode 38 are each connected to aseparate electrode lead wire 40. The electrode lead wires 40, which eachinclude an insulating coating, extend through the lead wire lumen 26 ofdistal shaft 14, the proximal shaft 12, and the deflection controlhandle 16, and terminate at their proximal end in an input jack (notshown) that may be plugged into an appropriate monitor (not shown). Inthe depicted embodiment, the portion of the electrode lead wires 40extending through the proximal shaft 12 and deflection control handle 16are enclosed within a protective sheath 42.

The electrode lead wires 40 are attached to the tip electrode 32 andring electrode 38 by any conventional technique. Connection of anelectrode lead wire 40 to the tip electrode 32 or ring electrode 38 ispreferably accomplished by welding the electrode lead wire's distal end,which is stripped of its insulative coating, to the corresponding tipelectrode or ring electrode.

A puller wire 44 is provided for deflection of the distal shaft 14. Thepuller wire 44 is anchored at its proximal end to the deflection controlhandle 16 and anchored at its distal end to the distal shaft 14, which.The puller wire 44 is made of any suitable metal, such as stainlesssteel or Nitinol, and is preferably coated with Teflon7 or the like. Thecoating imparts lubricity to the puller wire 44. The puller wire 44preferably has a diameter ranging from about 0.006 to about 0.010inches.

A compression coil 43 extends from the proximal end of the proximalshaft 12 to the proximal end of the distal shaft 14. The compressioncoil 43 is made of any suitable metal, preferably stainless steel. Thecompression coil 43 is tightly wound on itself to provide flexibility,i.e., bending, but to resist compression. The inner diameter of thecompression coil 43 is preferably slightly larger than the diameter ofthe puller wire 44. For example, when the puller wire 44 has a diameterof about 0.007 inches, the compression coil 43 preferably has an innerdiameter of about 0.008 inches. The Teflon7 coating on the puller wire44 allows it to slide freely within the compression coil 43. Along itslength, the outer surface of the compression coil 43 is covered by aflexible, non-conductive sheath 49 to prevent contact between thecompression coil 43 and any of the other components within the proximalshaft 12. A non-conductive sheath 49 made of polyimide tubing ispresently preferred. As shown in FIG. 2, the compression coil 43 isanchored at its proximal end to the proximal end of the proximal shaft12 by glue to form a glue joint 50 and at its distal end to the distalshaft 14 in the puller wire lumen 22 by glue to form a glue joint 52,but other arrangements are contemplated within the invention.

The puller wire 44 extends into the puller wire lumen 22 of the distalshaft 14. In the depicted embodiment, the puller wire 44 is anchored ina first blind hole 54 of the tip electrode 32. Preferably, a ferrule 41,made of stainless steel or the like, is crimped onto the distal end ofthe puller wire 44 to add thickness to the puller wire. The ferrule 41is then attached to the inside of the first blind hole 54 of the tipelectrode 32 with solder or the like. Alternatively, the puller wire 44can be anchored to the sidewall of the distal shaft 14. Within thedistal shaft 14, the puller wire 44 extends through into a plastic,preferably Teflon7, sheath 58, which prevents the puller wire 44 fromcutting into the wall of the distal shaft when the distal shaft isdeflected.

Longitudinal movement of the puller wire 44 relative to the proximalshaft 12, which results in deflection of the distal shaft 14, isaccomplished by suitable manipulation of the deflection control handle16. Examples of suitable control handles for use in the presentinvention are disclosed, for example, in U.S. Pat. Nos. Re 34,502,5,897,529 and 6,575,931, the entire disclosures of which areincorporated herein by reference. Other control handles capable ofaffecting longitudinal movement of the puller wire relative to thecatheter body can be used in the invention.

If desired, the catheter can include two or more puller wires (notshown) to enhance the ability to manipulate the distal shaft 14. In suchan embodiment, a second puller wire and a surrounding second compressioncoil extend through the proximal shaft 12 and into separate off-axislumens (not shown) in the distal shaft. Suitable deflection controlhandles for use with a catheter having more than one puller wire aredescribed in U.S. Pat. Nos. 6,123,699, 6,171,277, and 6,183,463, thedisclosures of which are incorporated herein by reference.

As shown in FIGS. 3 and 6, a needle electrode assembly 46 is providedwithin the catheter. The needle electrode assembly 46 is used to ablatetissue while simultaneously injecting saline or other fluid to conductthe ablation energy, thereby creating a theoretic increase in theeffective size of the electrode. The needle electrode assembly 46 isextendable and retractable, and may be moved by manipulation of theneedle control handle 17, as described further below. FIG. 3 depicts theneedle electrode assembly 46 in an extended position as it would be toablate tissue. The distal end of the needle electrode assembly 46 may bewithdrawn into the catheter to avoid injury, particularly during thetime that the catheter is inserted through the vasculature of the bodyand during the time in which the catheter is removed from the body.

The needle electrode assembly 46 comprises a proximal tubing 33 joined,directly or indirectly, to a generally rigid, electrically-conductivedistal tubing 35, as shown in FIG. 3. The generally rigid nature of thedistal tubing 35 allows it to pierce tissue in order to increase itseffectiveness during ablation. For example, the distal tubing 35 can beformed of Nitinol (or other nickel-titanium alloy), gold, platinum,stainless steel, or an alloy thereof, and, as illustrated in FIG. 3, ispreferably formed with a beveled edge 36 at the distal tip of the needleelectrode assembly 46 to enhance its ability to pierce tissue. Thediameter distal tubing 35 can vary, for example, from about 18 gauge toabout 29 gauge, and more particularly can be about 27 gauge. If desired,the distal tubing 35 can include one or more irrigation ports in itssidewall in addition to or instead of the opening at the distal end ofthe distal tubing. Such a design is described in U.S. Pat. No.6,575,931, the disclosure of which is incorporated herein by reference.

The proximal tubing 33 is preferably more flexible than the distaltubing 35 to allow the proximal tubing to bend as necessary with theflexible proximal shaft 13 of the catheter body 12, for instance whenthe catheter is inserted into the vasculature of the body. The proximaltubing 33 of the needle electrode assembly 46 is preferably made ofpolyimide or polyether etherketone (PEEK), but can be made of any othersuitable biocompatible material, such as plastic or metal.

A needle electrode lead wire 210 is electrically connected at its distalend to the electrically-conductive distal tubing 35 for supplying radiofrequency energy or other suitable ablation energy to the distal tubing.The needle electrode lead wire 210 is soldered, welded or otherwiseattached to the outside of the distal tubing 35, but could be attachedelsewhere to the distal tubing. The proximal end of the needle electrodelead wire 210 is attached to a suitable connector 67, which in turn isconnected to a suitable source of ablation energy (not shown).

Additionally, a temperature sensor is provided for measuring thetemperature of the tissue being ablated by the needle electrode assembly46 before, during or after ablation. Any conventional temperaturesensor, e.g., a thermocouple or thermistor, may be used. In the depictedembodiment, the temperature sensor comprises a thermocouple 200 formedby an enameled wire pair. One wire of the wire pair is a copper wire202, e.g., a number 40 copper wire. The other wire of the wire pair is aconstantan wire 204. The wires 202 and 204 of the wire pair areelectrically isolated from each other except at their distal ends, wherethey are twisted together, covered with a short piece of plastic tubing206, e.g., polyimide, and covered with epoxy, as shown in FIG. 7. Theplastic tubing 206 is then glued or otherwise attached to the insidewall of the distal tubing 35 of the needle electrode assembly 46. Theproximal ends of the wires 202 and 204 extend out the proximal end ofthe distal tubing 35 and are attached to an appropriate connector 67connectable to a suitable temperature monitor (not shown), as describedin more detail below. In an alternative embodiment, the copper wire 202of the thermocouple can also be used as the lead wire for the needleelectrode assembly 46. The temperature sensor can be eliminated ifdesired or can be mounted in any other part of the needle assembly 46,distal shaft 14 and/or tip electrode 32.

The proximal tubing 33 of the needle electrode assembly 46 extends fromthe needle control handle 17, through the deflection control handle 16,through the proximal shaft 13, and into the infusion lumen 24 of thedistal shaft 14. The proximal end of the distal tubing 35 is spacedslightly from the distal end of the proximal tubing 33 and extendsthrough the infusion lumen 30 of the distal shaft 14. The proximal anddistal tubings 33 and 35 are mounted, preferably coaxially, within anouter plastic tube 48. The outer plastic tube 48 can be glued orotherwise attached to the proximal and distal tubings to form a singlestructure that, as described below, is longitudinally moveable relativeto the catheter body 12. The outer plastic tube 48 extends through thecatheter body 12 with the proximal tubing and protects the needleelectrode lead wire 210 and thermocouple wires 202 and 204, which extendbetween the proximal tubing 33 and outer plastic tube 48, when theneedle electrode assembly 46 is moved relative to the distal shaft 14.The needle electrode lead wire 210 and thermocouple wires 202 and 204extend out through a hole (not shown) in the outer plastic tube 48within the deflection control handle 16 and are attached to appropriateconnectors, as noted above.

FIG. 6 shows one arrangement for joining the outer plastic tube 48 tothe proximal and distal tubings 33 and 35. Specifically, a small pieceof plastic tubing 45, for example, polyimide tubing, is placed over thediscontinuity between the proximal and distal tubings 33 and 35 andattached to the proximal and distal tubings by polyurethane glue or thelike to form a single infusion passage through which saline or otherfluid can pass from the proximal tubing to the distal tubing. The smallpiece of plastic tubing 45 helps to protect the thermocouple wires 202and 204 and the needle electrode lead wire 210. A small, preferablynon-conductive, spacer 51 is mounted between the distal tubing 35 andthe distal end of the outer plastic tube 48, and optionally glued inplace. The spacer 51 prevents bodily fluid from entering into the distalend of the needle electrode assembly 46. In FIG. 6, the relative sizesand positions of the tubings 33, 35, 45 and 48 are exaggerated forclarity.

In an exemplary embodiment, the proximal tubing 33 of the needleelectrode assembly 46 has an inner diameter of 0.014 inch and an outerdiameter of 0.016 inch. The distal tubing 35 has an inner diameter of0.014 inch and an outer diameter of 0.018 inch and a length of about 1.0inch. Further, the distal tubing 35 extends past the distal end of thedistal shaft 14 about 14 mm. The small plastic tubing 45 has an innerdiameter of 0.022 inch and an outer diameter of 0.024, the outer plastictube 48 has an inner diameter of 0.025 inch and an outer diameter of0.035 inch, and the plastic spacer 51 has an inner diameter of 0.017inch and an outer diameter of 0.024 inch.

Within the proximal shaft 12 and distal shaft 14, the needle electrodeassembly 46, comprising the proximal tubing 33, distal tubing 35, spacer51, plastic tubing 45 and outer plastic tube 48, is slidably mounted,preferably coaxially, within a protective tube 47 that is stationaryrelative to the catheter body. The protective tube 47 has a distal endglued into a passage 56 that extends through the tip electrode 32. Theprotective tube 47, which is preferably made of polyimide, serves toprevent the needle electrode assembly 46 from buckling during extensionand retraction of the needle electrode assembly relative to the catheterbody 12. The protective tube 47 additionally serves to provide afluid-tight seal surrounding the needle electrode assembly 46. Withinthe deflection control handle 16, the protective tube 47 and needleelectrode assembly 46 extend into a protective shaft 66, which ispreferably made of polyurethane.

Other needle electrode assembly designs are contemplated within thescope of the invention. For example, the needle electrode assembly cancomprise a single electrically-conductive tube, such as a Nitinol tube,that extends from the needle control handle 17 to the distal end of thecatheter. Such a design is described in U.S. patent application Ser. No.09/711,648, entitled “Injection Catheter with Needle Electrode,” thedisclosure of which is incorporated herein by reference.

Longitudinal movement of the needle electrode assembly 46 is achievedusing the needle control handle 17. The needle electrode assembly 46 andprotective tube 47 extend from the deflection control handle 16 to theneedle control handle 17 within the protective shaft 66.

As illustrated in FIG. 8, in one embodiment the needle control handle 17comprises a generally cylindrical outer body 80 having proximal anddistal ends, a piston chamber 82 extending a part of the waytherethrough, and a needle passage 83 extending a part of the waytherethrough. The piston chamber 82 extends from the proximal end of thehandle part way into the body 80, but does not extend out the distal endof the body. The needle passage 83, which has a diameter less than thatof the piston chamber 82, extends from the distal end of the pistonchamber to the distal end of the outer body 80.

A piston 84, having proximal and distal ends, is slidably mounted withinthe piston chamber 82. A proximal fitting 86 is mounted in and fixedlyattached to the proximal end of the piston 84. The proximal fitting 86includes a tubular distal region 87 that extends distally from the mainbody of the proximal fitting. The piston 84 has an axial passage 85through which the proximal tubing 33 of the needle electrode assembly 46extends, as described in more detail below. A compression spring 88 ismounted within the piston chamber 82 between the distal end of thepiston 84 and the outer body 80. The compression spring 88 can either bearranged between the piston 84 and outer body 80, or can have one end incontact with or fixed to the piston, while the other end is in contactwith or fixed to the outer body.

The proximal tubing 33, outer plastic tube 48, protective tube 47 andprotective shaft 66 extend from the deflection control handle 16 intothe distal end of the needle passage 83, as best shown in AREA A of FIG.8. Within the needle passage 83, the proximal tubing 33, outer plastictube 48, protective tube 47 and protective shaft 66 extend into a firstmetal tube 90, which is preferably made of stainless steel. If desired,the first metal tube 90 could instead be made of a rigid plasticmaterial. The first metal tube 90 is secured to the outer body 80 of theneedle control handle 17 by a set screw 101 or any other suitable means.The protective shaft 66 terminates at its proximal end within the firstmetal tube 90.

A second metal tube 91 is provided with its distal end mounted,preferably coaxially, inside the proximal end of the first metal tube 90and with its distal end abutting the proximal end of the protectiveshaft 66. The second metal tube 91 is fixed in place relative to thefirst metal tube 90 by the set screw 101. The second metal tube 91, likethe first metal tube 90, could alternatively be made of a rigid plasticmaterial.

The proximal end of the second metal tube 91 is mounted, preferablycoaxially, around the distal end of the tubular distal region 87 of theproximal fitting 86, with the second metal tube being longitudinallymovable relative to the tubular distal region 87. Accordingly, when thepiston 84 is moved distally relative to the outer body 80, the tubulardistal region 87 moves distally into the second metal tube 91. As shownin AREA B of FIG. 8, the proximal tubing 33 and outer plastic tube 48extend through the second metal tube 91 and into the tubular distalregion 87 of the proximal fitting 86. The outer plastic tube 48terminates in and is fixedly attached to the proximal fitting 86 tothereby attach the outer plastic tube, and thus the needle electrodeassembly 46, to the piston 84. Within the proximal fitting 86, theproximal tubing 33 extends out of the outer plastic tube 48 and into afirst protective sheath 31, as shown in AREA C of FIG. 8, and isconnected to a luer connector 65, which is connected to an irrigationpump or other suitable fluid infusion source (not shown), as is known inthe art. Similarly, the needle electrode lead wire 210 and thethermocouple wires 202 and 204 extend out of the outer plastic tube 48and into a second protective sheath 29, as also shown in AREA C of FIG.2, which is connected to a suitable connector 67, such as a 10-pinelectrical connector, for connecting the needle electrode lead wire to asource of ablation energy and the thermocouple wires to a suitablemonitoring system.

In use, force is applied to the piston 84 to cause distal movement ofthe piston relative to the outer body 80, which compresses thecompression spring 88. This movement causes the needle electrodeassembly 46 to correspondingly move distally relative to the outer body80, protective shaft 66, protective tube 47, proximal shaft 13, anddistal shaft 14 so that the distal tubing 35 of the needle electrodeassembly extends outside the distal end of the distal shaft. When theforce is removed from the piston 84, the compression spring 88 pushesthe piston proximally to its original position, thus causing the distaltubing 35 of the needle electrode assembly 46 to retract back into thedistal end of the distal shaft 14. Upon distal movement of the piston84, the tubular distal region 87 of the proximal fitting 86 movesdistally into the second metal tube 91 to prevent the proximal tubing 33and the outer plastic tube 48 of the needle electrode assembly 46 frombuckling within the axial passage 85.

The piston 84 further comprises a longitudinal slot 100 extending alonga portion of its outer edge. A securing means 102, such as a set screw,pin, or other locking mechanism, extends through the outer body 80 andinto the longitudinal slot 100. This design limits the distance that thepiston 84 can be slid proximally out of the piston chamber 82. When theneedle electrode assembly 46 is in the retracted position, preferablythe securing means 102 is at or near the distal end of the longitudinalslot 100.

The proximal end of the piston 84 has a threaded outer surface 104. Acircular thumb control 106 is rotatably mounted on the proximal end ofthe piston 84. The thumb control 106 has a threaded inner surface 108that interacts with the threaded outer surface 104 of the piston. Thethumb control 106 acts as a stop, limiting the distance that the piston84 can be pushed into the piston chamber 82, and thus the distance thatthe needle electrode assembly 46 can be extended out of the distal endof the catheter. The threaded surfaces of the thumb control 106 andpiston 84 allow the thumb control to be moved closer or farther from theproximal end of the outer body 80 so that the extension distance of theneedle electrode assembly 46 can be controlled by the physician. Asecuring means, such as a tension screw 110 is provided in the thumbcontrol 106 to control the tension between the thumb control and piston84. As would be recognized by one skilled in the art, the thumb control106 can be replaced by any other mechanism that can act as a stop forlimiting the distance that the piston 84 extends into the piston chamber82, and it is not necessary, although it is preferred, that the stop beadjustable relative to the piston.

Additionally, a location sensor 70 is contained within the distal end ofthe distal shaft 14. The location sensor 70 is used to determine thecoordinates of the distal end of the catheter, for example, duringmapping of electrical activity or during placement of the distal end ofthe catheter for ablation. In the depicted embodiment, a single locationsensor 70 is mounted in the distal end of the distal shaft 14, partlywithin a second blind hole 55 in the tip electrode 32 and partly withinthe plastic housing 34.

The location sensor 70 is connected to a corresponding sensor cable 72.The sensor cable 72 extends through proximal shaft 12 and deflectioncontrol handle 16 and out of the proximal end of the deflection controlhandle within an umbilical cord (not shown) to a sensor control module(not shown) that houses a circuit board (not shown). Alternatively, thecircuit board can be housed within the deflection control handle 16, forexample, as described in U.S. Pat. No. 6,024,739, the disclosure ofwhich is incorporated herein by reference. The sensor cable 72 comprisesmultiple wires encased within a plastic covered sheath. In the sensorcontrol module, the wires of the sensor cable 72 are connected to thecircuit board. The circuit board amplifies the signal received from thelocation sensor 70 and transmits it to a computer in a formunderstandable by the computer by means of a sensor connector at theproximal end of the sensor control module. Also, because the catheter isdesigned for single use only, the circuit board preferably contains anEPROM chip that shuts down the circuit board approximately twenty-fourhours after the catheter has been used. This prevents the catheter, orat least the location sensor 70, from being used twice.

Preferably the location sensor 70 is an electromagnetic location sensor.For example, the location sensor 70 may comprise amagnetic-field-responsive coil, as described in U.S. Pat. No. 5,391,199,or a plurality of such coils, as described in International PublicationWO 96/05768. The plurality of coils enables the six-dimensionalcoordinates (i.e. the three positional and the three orientationalcoordinates) of the location sensor 70 to be determined. Alternatively,any suitable location sensor known in the art may be used, such aselectrical, magnetic or acoustic sensors. Suitable location sensors foruse with the present invention are also described, for example, in U.S.Pat. Nos. 5,558,091, 5,443,489, 5,480,422, 5,546,951, and 5,568,809,International Publication Nos. WO 95/02995, WO 97/24983, and WO98/29033, and U.S. patent application Ser. No. 09/882,125 filed Jun. 15,2001, entitled “Position Sensor Having Core with High PermeabilityMaterial,” the disclosures of which are incorporated herein byreference.

Using this technology, the physician can visually map a heart chamber.This mapping is done by advancing the distal shaft 14 into a heartchamber until contact is made with the heart wall. This position isrecorded and saved. The distal shaft 14 is then moved to anotherposition in contact with the heart wall and again the position isrecorded and saved.

The electromagnetic mapping sensor 70 can be used alone or, morepreferably, in combination with the tip electrode 32 and/or ringelectrode 38. By combining the electromagnetic sensor 70 and electrodes32 and 38, a physician can simultaneously map the contours or shape ofthe heart chamber, the electrical activity of the heart, and the extentof displacement of the catheter.

It is understood that, while it is preferred to include bothelectrophysiology electrodes (such as the tip electrode 32 and ringelectrode 38) and an electromagnetic sensor in the distal shaft 14, itis not necessary to include both. For example, an ablation catheterhaving an electromagnetic sensor but no electrophysiology electrodes maybe used in combination with a separate mapping catheter system. Apreferred mapping system includes a catheter comprising multipleelectrodes and an electromagnetic sensor, such as the NOGA-STAR cathetermarketed by Biosense Webster, Inc., and means for monitoring anddisplaying the signals received from the electrodes and electromagneticsensor, such as the Biosense-NOGA system, also marketed by BiosenseWebster, Inc.

The catheters in accordance with the present invention are particularlysuitable for ablating large, deep lesions in heart tissue. In operation,the distal end of the catheter is inserted into a vein or artery andadvanced into the heart. To assist in positioning the distal shaft 14 ofthe catheter at a desired position within the heart, the puller wire 50and deflection control handle 16 are used to deflect the distal shaft14. Once the distal shaft 14 has been positioned at or near the desiredlocation of the heart tissue, and preferably arranged generallyperpendicular to the heart tissue, the distal end of the needleelectrode assembly 46 is advanced distally, using the needle controlhandle 17, out of the distal end of the catheter and into the adjacentheart tissue.

The depth to which the distal end of the needle electrode assembly 46 isadvanced into the heart tissue can vary depending on the desired size ofthe lesion to be produced. For example, the depth of the needlepenetration can range from about 2 to about 30 mm, more particularlyfrom about 3 to about 20 mm, still more particularly from about 4 toabout 10 mm, even more particularly from about 5 to about 7 mm. Thedeeper the needle is advanced, the more needle surface area that isprovided for ablation, but the greater the risk of perforation. Theneedle is preferably advanced a sufficient distance so that fluidinfused through the needle goes into the heart tissue.

Fluid is then infused through the needle ablation assembly 46, beforeand/or during ablation, to enhance the ablation by serving as a virtualelectrode. The fluid used should be biologically acceptable and shouldbe able to conduct ablation energy from the needle electrode to theheart tissue. Preferably the fluid used is saline having a salt contentranging from about 0.3 to about 4 wt %, more particularly from about 0.5to about 3 wt %, still more particularly from about 0.9 to about 2.5 wt%, even more particularly from about 0.9 to about 1.5 or 2 wt %.

If desired, the saline or other fluid being infused through can includea radiographic contrast agent, preferably comprising an iodinatedcompound, such as an iodinated contrast with diatrizoate salt withmeglumine and sodium or an ioxaglate salt with meglumine and sodium; ora nonionic contrast with iohexol, iopamidol, iopromide, and/or ioversol.If used, the amount of contrast media present in the fluid can vary asdesired, and can range, for example, from about 5 to about 50%, moreparticularly from about 10 to about 30%, still more particularly fromabout 10 to about 20%. The contrast agent permits theelectrophysiologist to view the relative location of the distal end ofthe needle electrode, thereby providing both evidence concerningadequate tissue penetration and reassurance that the needle electrodehas not penetrated all the way through the myocardium into thepericardium. The contrast agent also gives the electrophysiologist anindication of the approximate size and shape of the lesion that will becreated.

The flow rate of the fluid through the needle ablation assembly and theduration of infusion can vary depending on the desired lesion size andthe size of the distal tubing of the needle, i.e., that part of theneedle introduced into the tissue. For example, saline or other fluidcan be infused through the needle ablation assembly into the hearttissue at a rate ranging from about 0.3 to about 5 ml/min, moreparticularly from about 0.3 to about 3 ml/min, still more particularlyfrom about 0.8 to about 2.5 ml/min, still more particularly from about 1to about 2 ml/min. If infusing prior to ablation, preferably the fluidis not infused for more than a minute prior to beginning ablation.

Ablation energy, preferably radio frequency, is then applied to thedistal tubing 35 of the ablation needle assembly 46 though the needleelectrode lead wire 210. The amount of energy can vary depending on thedesired lesion size, and can be, for example, up to about 100 watts,more particularly up to about 70 watts, still more particularly fromabout 20 to about 50 watts, even more particularly from about 30 toabout 40 watts. The duration of the ablation, i.e., the duration thatthe radio frequency energy is delivered to the needle electrode and thusto an area of tissue through the needle electrode and through the salineor other fluid passing through the needle electrode, can also vary onthe size of the desired lesion. It has been found that substantiallesions can be created with a duration of ablation that need not besignificantly longer than about 120 seconds. Preferably the duration ofablation is at least about 15 seconds, more preferably at least about 30seconds, and may last as long as 60 seconds, 90 seconds or more.

If the needle electrode is used for ablation without prior orsimultaneous fluid of an ionically-conductive fluid, the lesion sizewill not be as large, and the amount of power cannot be as high as withthe infusion of the fluid. For example, for a needle electrode withoutsaline infusion, the power should not exceed about 5 to 10 watts toavoid charring, whereas much more power can be delivered with fluidinfusion without significant charring. The saline or other fluidpermeates between the muscle fibers and spreads out from the needleelectrode puncture site. As a result, the electrical resistance isspread over a larger area. The resulting lesion is typically generallyspherically-shaped.

If desired, a surface lesion can be burned with the tip electrode 32before, during and/or after a lesion is created with the needleelectrode to increase the size of the endocardial portion of theablation and create a more bullet-shaped lesion. In an alternativemethod, the needle electrode is used only to infuse saline into theheart tissue, and the tip electrode is the used to ablate a burn fromthe tissue surface.

Impedance can be measured through the needle electrode, for example, bythe radio frequency energy generator, as is generally known in the art.The impedance measurement can be used to vary the flow rate of thesaline or other fluid, the amount of power delivered, and/or the timethat the fluid is infused and/or the power delivered. If desired, afeedback control loop can be created.

Similarly, the temperature of the tissue can be indirectly measured bymeasuring the temperature of the distal tubing 35 of the ablation needleassembly 46 using the temperature sensor mounted in the distal tubing.The temperature measurement can similarly be used to vary the flow rateof the saline or other fluid, the amount of power delivered, and/or thetime that the fluid is infused and/or the power delivered, and afeedback control loop can be created. Preferably the temperature of thedistal tubing 35 ranges from about 35 to about 90° C., more preferablyfrom about 45 to about 80° C., still more preferably from about 55 to70° C. If desired, a portion of the distal tubing 35 of the needleablation assembly 46 can be coated or covered with an insulatingmaterial. Preferably the distal end region, e.g., about 1 to about 30mm, more particularly from about 2 to about 20 mm, even moreparticularly from about 3 to about 12 mm, of the distal tubing 35 isexposed, i.e., remains electrically conductive, and a region proximal tothe distal end region is covered with the insulating material. With thisdesign, ablation energy can be delivered to the tissue without beingdelivered at the endocardial surface to avoid overheating at theendocardial surface, which can cause clotting.

The distal tubing 35 of the needle ablation assembly 46, the tipelectrode 32 and/or any ring electrodes 38 can be used to measure andrecord electrical activity. In particular, the electrical activity canbe measured before ablation to confirm that the tissue should beablation and/or after ablation to confirm that the ablation had thedesired effect on the tissue, e.g., that the electrical activity in thattissue has been changed or eliminated. The distal tubing 35 of theneedle ablation assembly 46 and/or the tip electrode 32 can also be usedfor pacing, for example, to determine whether tissue is viable beforeablating and/or to determine whether the ablation had the desiredeffect.

EXAMPLES

The following examples show suitable ablation methods according to theinvention. Experiments were conducted in vitro using bovine myocardium,and in vivo using swine and goats.

Example 1 In Vitro Needle Ablation Studies

Feasibility studies of delivery of radiofrequency (RF) ablative energyto tissue using a catheter having a needle electrode were carried outusing bovine myocardium in room temperature 0.9% NaCl solution. RFenergy was delivered using a Stockert 70 RF generator. Tissueoverheating and pops occurred at relatively low power outputs. Steampops tended to occur when power was higher, but this did not reachstatistical significance (p=0.183). See FIG. 9. It was determined thatlesions could be created and had depth to the full extent of needlepenetration, but lesion diameter was limited by impedance rises andtissue overheating, with subsequent current limitation. RF lesiondiameter increased with average power delivered and with maximum powerdelivered. Lesion size plateaued after 30 to 60 seconds of RFapplication, and increased with power delivered, reaching a plateau at 8to 10 Watts. See FIG. 10. Lesion depth was limited only by needlelength.

Example 2 In Vivo Needle Ablation Studies

In vivo temperature-controlled needle ablation lesions were performed inanaesthetized swine. The catheter was introduced into femoral vesselsand navigated using fluoroscopy and electroanatomic mapping. The distalend was placed in contact with and perpendicular to the endocardium. Theneedle electrode was extended 10 mm, and RF energy (500 kHz, Stockert-70RF Generator, Freiburg, Germany) was delivered between the needleelectrode and a skin electrode for 120 second applications. Temperaturewas monitored using the thermocouple within the needle electrode, andpower was titrated manually to maintain temperature at or below 90° C.Control lesions were created with a standard ablation catheter undertemperature control titrated to maintain tip temperature at or below 60°C. for 120 second applications. Thirteen needle ablations and ninecontrol lesions were available for analysis. The animal was sacrificed,and the lesions were identified and excised. They were formalin-fixedand serially sectioned from the endocardium and digitally imaged forquantitative analysis. Needle ablation lesions had a characteristicappearance with minimal endocardial disruption, and a small circulararea of pallor. The cut surfaces revealed a long narrow lesion extendingthe full length of the needle track with a uniform diameter. Controllesions had an ovoid area of pallor on the surface, slight wideningwithin the first 2 mm of depth, and then rapid tapering. Needle lesionswere significantly deeper than control lesions but of smaller volume.See Table 1, below, and FIG. 11.

TABLE 1 In Vivo Needle Ablation Results Needle Lesions Control LesionsMean Depth 10.2 ± 0.8 mm 5.7 ± 0.4 mm p < 0.001 Likelihood 77% 11% p =0.008 Transmural Mean Volume 175 ± 18 mm³ 358 ± 56 mm³ p = 0.02 Maximal7 ± 0.4 mm 12 ± 0.7 mm p < 0.001 Diameter (mean)

Example 3 In Vitro Needle Infusion Ablation Studies

In order to increase lesion dimension, the size of the area of resistiveheating needed to be increased. Infusion of ionic solution through theneedle electrode into the tissue of interest increased the size of thevirtual electrode, increasing conductance in the area immediatelysurrounding the ablating needle electrode. This shifts the site of thesteepest gradient of resistance, and thus the zone of resistive heatingfarther from the electrode and creates a larger area of resistiveheating, and consequently a larger area of conductive heating. Bovinemyocardium strips were immersed in ionic solution at room temperature.The needle electrode was deployed within the tissue, and 0.9% NaClsolution was infused at 1 mL/minute and 2 mL/minute with serialobservations of the impedance recorded. The initial impedance fell byapproximately 20 ohms during the first 20 seconds of infusion and thenrelatively plateaued during the rest of 120 seconds of infusion. SeeFIG. 12.

Further studies demonstrated in vitro that with a preinjection of 0.9%NaCl of up to 60 seconds at 1 mL/min, and with continued 1 mL/mininfusion during RF and power set at 10 W, lesion size plateaued atapproximately 120 seconds. Lesions created in this manner weresignificantly larger than those created without saline infusion. SeeFIG. 13.

Example 4 In Vivo Needle Infusion Ablation Studies

In ten anaesthetized swine, the left ventricle was entered using thecatheter via the femoral artery and directed using electroanatomicmapping and fluoroscopy. The distal end of the catheter was positionedperpendicularly to the endocardial surface, and the needle electrode wasadvanced 5 to 7 mm into the myocardium. 0.9% NaCl solution was infusedat 1 mL/min intramyocardially for 60 seconds, and RF was delivered viathe needle electrode for 120 seconds during ongoing infusion. Power wastitrated to 30 to 40 Watts, adjusted to avoid impedance rises. At theend of the procedure, the heart was excised, and the lesions wereidentified, excised and formalin fixed. They were then seriallysectioned from the endocardium and digitally imaged for quantitativeanalysis. Lesion volume was calculated. Lesions were compared tostandard endocardial ablation lesions created under power control,titrated to achieve a 10 ohm impedance fall using a 4 mm tip catheter.Needle infusion ablation lesions were significantly deeper thancontrols, more likely to be transmural and had significantly largervolumes and cross-sectional areas at each millimeter of depth beyond theendocardium. See Table 2 and FIG. 14.

TABLE 2 Saline Needle Infusion In Vivo Needle/Infusion Control MeanDepth 13 ± 2 mm 5 ± 1 mm P < 0.001 Likelihood 41% 11% P = 0.03Transmural Volume 1600 ± 100 mm³ 240 ± 40 mm³ P < 0.001

The preceding description has been presented with reference to presentlypreferred embodiments of the invention. Workers skilled in the art andtechnology to which this invention pertains will appreciate thatalterations and changes in the described structure may be practicedwithout meaningful departing from the principal, spirit and scope ofthis invention. For example, the tip electrode can be eliminated ifdesired. The location sensor could also be eliminated, in which caseanother mapping method, such as ultrasound, could optionally be used todetermine the location of the catheter. Accordingly, the foregoingdescription should not be read as pertaining only to the precisestructures and methods described and illustrated in the accompanyingdrawings, but rather should be read consistent with and as support tothe following claims which are to have their fullest and fair scope.

What is claimed is:
 1. A method for ablating tissue in or around theheart comprising: introducing into the heart a distal end of a catheter,the catheter comprising: a proximal shaft, a distal shaft distal theproximal shaft and comprising a distal shaft tubing having an infusionlumen and at least one second lumen off-axis from the infusion lumen,the distal shaft terminating in the distal end of the catheter, and aneedle electrode assembly, the needle electrode assembly comprising aproximal tubing having a distal end longitudinally spaced from andaligned with a proximal end of a distal tubing, wherein fluid can passfrom the distal end of the proximal tubing to a longitudinal spacebetween the distal end of the proximal tubing and the proximal end ofthe distal tubing to the proximal end of the distal tubing, the proximaltubing being more flexible than the distal tubing, wherein the distaltubing comprises at least one irrigation port in a sidewall of thetubing, the proximal tubing extending through the proximal shaft intothe infusion lumen in the distal shaft, the distal tubing of the needleelectrode assembly being in a retracted position within the distalshaft, the needle electrode assembly further comprising an outer tubingin which the distal end of the proximal tubing and the proximal end ofthe distal tubing are fixedly mounted to form a single structure that islongitudinally moveable relative to the proximal shaft; introducing adistal end of the distal tubing of the needle electrode assembly intothe tissue, including moving the distal tubing from its retractedposition within the distal shaft to an extended position outside thedistal shaft; infusing into the tissue an electrically-conductive fluidthrough the distal tubing of the needle electrode assembly while in theextended position; and ablating the tissue after and/or duringintroduction of the fluid into the tissue, whereby the fluid conductsablation energy within the tissue to create a larger lesion than wouldbe created without the introduction of the fluid.
 2. The methodaccording to claim 1, wherein the distal tubing of the needle electrodeassembly comprises a closed distal face.
 3. The method according toclaim 1, wherein the distal tubing of the needle electrode assemblycomprises an opening at a distal face of the tubing.
 4. The methodaccording to claim 1, wherein the tissue is ablated using the needleelectrode assembly.
 5. The method according to claim 1, wherein thetissue is ablated using a tip electrode on the distal end of thecatheter.
 6. The method according to claim 1, wherein the fluid isinfused through the needle electrode assembly during ablation.
 7. Themethod according to claim 1, wherein the fluid is infused through theneedle electrode assembly before ablation.
 8. The method according toclaim 1, wherein the fluid is infused through the needle electrodeassembly before and during ablation.
 9. The method according to claim 1,wherein the fluid infused through the needle electrode assemblycomprises saline having a salt content ranging from about 0.3 to about 4wt %.
 10. The method according to claim 1, wherein the fluid infusedthrough the needle electrode assembly comprises a radiographic contrastagent.
 11. The method according to claim 10, wherein the amount of thecontrast agent present in the fluid ranges from about 5 to about 50%.12. The method according to claim 1, wherein the fluid is infusedthrough the needle electrode assembly at a rate ranging from about 0.3to about 5 ml/min.
 13. The method according to claim 1, wherein radiofrequency energy is introduced to the needle electrode assembly at apower up to about 70 watts.
 14. The method according to claim 1, whereinradiofrequency energy is introduced to the needle electrode assembly forat least about 15 seconds.
 15. The method according to claim 4, furthercomprising burning a surface lesion with a tip electrode on thecatheter, wherein the surface lesion is burned at an endocardial surfaceof the tissue ablated with the needle electrode assembly.
 16. The methodaccording to claim 1, further comprising taking an impedance measurementusing the needle electrode assembly before, during and/or afterintroduction of the distal end of the needle electrode assembly into thetissue.
 17. The method according to claim 16, further comprisingadjusting a flow rate of the fluid infused through the needle electrodeassembly, and/or an amount of power delivered to the needle electrodeassembly, and/or the time over which the fluid is infused and/or thepower delivered in response to the impedance measurement.
 18. The methodaccording to claim 1, further comprising measuring a temperature of theneedle electrode assembly during ablation.
 19. The method according toclaim 18, further comprising adjusting a flow rate of the fluid infusedthrough the needle electrode assembly, and/or an amount of powerdelivered to the needle electrode assembly, and/or the time over whichthe fluid is infused and/or the power delivered in response to thetemperature measurement.
 20. The method according to claim 19, whereinthe needle electrode assembly is maintained at a temperature rangingfrom about 35 to about 90° C.
 21. The method according to claim 1,further comprising measuring electrical activity using the needleelectrode assembly before and/or after ablation.
 22. The methodaccording to claim 1, further comprising pacing using the needleelectrode assembly before and/or after ablation.